1. Field of the Invention
The present invention relates to new profiles for use as reinforcement or bordering of sheetlike composite elements ("sandwich elements"), to the composite elements constructed with these profiles, and to a process for producing these composite elements.
2. Background Art
Sheetlike composite elements, consisting most simply of a core layer and two top layers connected by this core layer and surface-bonded to it, the material employed for the core layer generally being a rigid foam and the material employed for the top layers generally being sheet metal or another material having tensile strength, are increasingly used as a construction material owing to their low weight and advantageous mechanical properties. In transportation in particular, i.e. in the construction of commercial vehicles of all kinds, for example lorries, buses or rail vehicles, or of freight containers, they are employed in particular for floor, wall and ceiling constructions.
Here and in the text below the term "sheetlike" composite elements does not refer exclusively to flat components but also to curved parts, such as the roofs of rail carriages, whose form can essentially be described by cylindrical areas or by a combination of flat and cylindrical areas.
Owing to the limited stability of these composite elements in the case of locally concentrated stresses, especially as a result of forces acting in a punctiform or linear manner perpendicularly to the layers and above all in the border region, it is frequently necessary to install reinforcing elements at the appropriate points, i.e. places where fixing elements need to be attached to join the composite elements to one another, to other load-bearing structural components or to mechanically stressed fitments (e.g. seats, holding rails or luggage racks in public transport vehicles), these reinforcing elements being in the form of profiles of metal or another high-strength material.
The term border profiles is used here and below to denote those profiles which form the border of a composite element or which join two composite elements to one another at their borders (joining profiles). Insert profiles denote those profiles which for reinforcement purposes are arranged in the interior of the composite element, the core layer being interrupted at the appropriate point and the top layers running on over the profile.
Both the core layer and the top layers can be homogeneous or can be constructed in turn from a plurality of layers. For example, a reinforcing layer can be embedded in a core layer of foam, or a top layer may, for example, consist of plywood.
The composite elements are normally produced by coating one or both sides of the top layers (consisting for example of sheet aluminium), the core material and the insert or border profiles--having simple cross-sections, in general, usual square profiles--with an adhesive, initially on the boundary faces. Subsequently, the individual parts are brought together in the desired geometric arrangement in a bonding mould and surface-bonded by external pressure. The external pressure employed is frequently the atmospheric air pressure, the bonding mould being covered with an airtight film and evacuated. In order to obtain a good bond and a flawless surface, it is necessary to allow the air between the layers, and also any excess adhesive, to escape as fully as possible. To this end the core layer is often provided with a relatively large number of parallel slots or grooves through which the air is able to pass to the border of the composite element. When using customary commercial profiles, for example in U, Z or H cross-section, however, this is no longer ensured. Indeed, in order to achieve high mechanical stability these profiles must be bonded over their entire area both to the top layers and to the narrow side of the core layer, leaving no room in between for the escape of air. Consequently, the production of composite elements of large surface area in particular is often accompanied, especially in the region of the profiles, by the formation of air bubbles, which may considerably impair the mechanical properties and may also be visible on the exterior of the component.